Code Editor - Support custom keybinding

[zamoore]

📌 Summary

If merged, this PR adds support for custom keybinding through the extraKeys argument.

🛠️ Detailed description

Many of our consumers code editors have custom keybinding through the extraKeys argument, which was a setting in CodeMirror 5

{{code-mirror
  screenReaderLabel="Namespace definition"
  theme="hashi"
  mode="javascript"
  content=this.definitionString
  onUpdate=this.updateNamespaceDefinition
  autofocus=false
  extraKeys=(hash Cmd-Enter=this.save) <- here
}}

This duplicates that same API but with our CodeMirror 6 implementation.

🔗 External links

Jira ticket: HDS-4672

---

👀 Component checklist

• Percy was checked for any visual regression
• A changelog entry was added via Changesets if needed (see templates here)

💬 Please consider using conventional comments when reviewing this PR.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
hds-showcase	✅ Ready (Inspect)	Visit Preview	Mar 18, 2025 8:05pm
hds-website	✅ Ready (Inspect)	Visit Preview	Mar 18, 2025 8:05pm

[shleewhite]

Looks good, we should recommend in the docs that if they add custom key binding theres a couple things to consider:

• there should be information visible on the page that lets users know they can use the shortcut
• they should never use single key shortcuts (ie. 's' to save) because that violates WCAG 2.1.4